1. Field of the Invention
The present invention relates to a dry-type developer material for developing latent electrostatic images to visible images, for use in electrophotography, electrostatic recording methods and electrostatic printing methods.
2. Description of Related Art
Developer material compositions containing charge-enhancing additives are known in the prior art, particularly those developers containing charge-enhancing additives which impart a positive charge to the toner resin. However, few developing compositions are known in the art wherein charge-enhancing additives are employed for the purpose of imparting a negative charge to the toner resin.
U.S. Pat. No. 3,893,935 discloses use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. According to this disclosure, certain quaternary ammonium salts, when incorporated into toner materials, were found to provide a toner composition exhibiting relatively high uniform and stable net toner charge when mixed with a suitable carrier.
U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is used, namely a diazo-type compound.
U.S. Pat. No. 4,411,974 discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge-enhancing additive, ortho-halo phenyl carboxylic acids.
U.S. Pat. No. 4,206,064 discloses toner compositions which are chromium, cobalt and nickel complexes of salicylic acid, as negative charge-enhancing additives.
U.S. Pat. No. 4,415,646 discloses a polymeric charge-enhancing additive resulting from the condensation reaction of maleic anhydride polymers with certain alkyl diamines, followed by quaternizing the resulting product.
U.S. Pat. No. 4,623,606 discloses a toner composition comprised of resin particles, pigment particles and iron complex charge-enhancing additives. Among the cations said to be useful with the iron complex charge-enhancing additives were hydrogen, sodium, potassium, ammonium, substituted ammonium, including aliphatic, alicyclic and heterocyclic ammonium.
U.S. Pat. No. 4,433,040 discloses an electrophotographic toner containing a metal complex die in which the metal complex contains a chromium or a cobalt atom. The metal complex die of the foregoing reference is a two-to-one type metal complex die with the negative charge neutralized by a cationic moiety, specifically by a hydrogen atom. The materials of this reference were alleged to exhibit remarkably high compatibility with the binder resin.
U.S Pat. No. 4,624,907 further discloses a charge-controlling and coloring agent comprising a two-to-one type metal complex die similar to that of the U.S. Pat. No.4,433,040. However, in the subject disclosure, the cationic material is an ammonium ion, an aliphatic ammonium ion, an alicyclic ammonium ion, or a heterocyclic ammonium ion, while the metal is a chromium, cobalt or iron atom.
Although the aforementioned references, the disclosures of which are incorporated by reference herein, provide outstanding performance as negative charge control agents, there remains a need for materials which have substantially improved compatibility with resin formulations, as well as exhibiting superior triboelectric properties.
It is, therefore, an object of this invention to provide a superior charge control agent which has an optimum combination of charging capacity and compatibility with binder resin.
Many of the negative charge control agents described in the literature are salts of a large negative anion, wherein the negative charge is diffused over numerous atoms, and a countercation, such as hydrogen, ammonium, lithium, sodium or potassium. Since the mechanism of charging is not well understood, the discovery and exploitation of new negative charge control agents is extremely difficult. The art has focused upon attempts to modify or uncover new anionic materials as charge control agents. It has now been discovered, however, that modification of the cationic portion of the agent will provide significantly enhanced performance in toner compositions.